Recently we have found that mtiogen- or antigen-stimulated T-lymphocytes produce a T-cell growth factor (TCGF) that allows for the maintenance of cytotoxic T-cells in continuous exponential proliferation. The TCGF is not species-specific and is consumed by proliferating T-cells. The proposed research is concernd with the charaterization of TCGF, the initiation and functionl characterization of cytotoxic, helper, and suppressor T-cell lines and the production of functional T-cell hybrids. The cellular origin, immunochemical nature, and in vitro as well as in vivo biologic activity of TCGF will be determined. Cytotoxic as well as helper and suppressor T-cells lines will be cloned and characterized as to their phenotypic and functional characteristics. Unifunctional continuous T-cell lines will then be used to produce antisera to differentiation antigens and to create functional T-cell hybrids.